There are two usages of "external world", as depicted by the mobile device metaphor that substitutes for brain / body. The outer environment featured on the screen (corresponding to conscious experience) and the outer environment which it represents (existing independently of the mobile device). Shifting from mobile devices to humans, the empirical external world is immediate and "just there" with its manifested evidence; the second or metempirical one is inferred by our extended, reflective thought (intellectual evidence). Obviously, due to the experienced outer world being "housed" within "consciousness" (whatever that is), the latter only has its brain / body correlate turning the corner in its visual manifestations of such.

Immanual Kant wrote:The expression 'outside us' is . . . unavoidably ambiguous in meaning, sometimes signifying what as thing in itself exists apart from us, and sometimes what belongs solely to outer appearance. . . . We can indeed admit that something, which may be (in the transcendental sense) outside us, is the cause of our outer intuitions. But this is not the object of which we are referring to in the presentations of matter and of corporeal things. For these are merely appearances, that is, mere kinds of representation, which are never to be met with save in us. . . . [CPR]

However, a product is not always trying to represent its cause or provenance. Is a computer game reality as exhibited on a monitor a representation of the computer? Is a dream a representation of the brain? But humans simply have a preference for duality or plurality or duplication. Which in turn repeats themselves in that higher, "true world" they speculate about; or even eradicates them as illusion in it, if that's their particular bag of angst.

So even though cause does not imply representation, the majority choose that to be the case in this instance; and then blame the mediating agencies and processes for doing an an inaccurate or sloppy or a deceptive job of it. "This material wall I just ran into is not a wall! It's empty space and force fields, etc! It's a fable of wall-dom superimposed over a flux of quantum particles, etc!"

David Chalmers wrote:In the Garden of Eden, we had unmediated contact with the world. We were directly acquainted with objects in the world and with their properties. Objects were simply presented to us without causal mediation, and properties were revealed to us in their true intrinsic glory.

When an apple in Eden looked red to us, the apple was gloriously, perfectly, and primitively red. There was no need for a long causal chain from the microphysics of the surface through air and brain to a contingently connected visual experience. Rather, the perfect redness of the apple was simply revealed to us. The qualitative redness in our experience derived entirely from the presentation of perfect redness in the world.

Eden was a world of perfect color. But then there was a Fall.

First, we ate from the Tree of Illusion. After this, objects sometimes seemed to have different colors and shapes at different times, even though there was reason to believe the object itself had not changed. So the connection between visual experience and the world became contingent: we could no longer accept that visual experience always revealed the world exactly as it is.

Second, we ate from the Tree of Science. After this, we found that when we see an object, there is always a complex causal chain involving the transmission of light from the object to the retina, and the transmission of electrical activity from the retina to the brain. This chain was triggered by microphysical properties whose connection to the qualities of our experience seemed entirely contingent. So there was no longer reason to believe in acquaintance with the glorious primitive properties of Eden, and there was no reason to believe that objects in the world had these properties at all.

We no longer live in Eden. Perhaps Eden never existed, and perhaps it could not have existed. But Eden still plays a powerful role in our perceptual experience of the world. At some level, perception represents our world as an Edenic world, populated by perfect colors and shapes, with objects and properties that are revealed to us directly. And even though we have fallen from Eden, Eden still acts as a sort of ideal that regulates the content of our perceptual experience. [Perception and the Fall from Eden]

Another spin to this: Knowledge is the qualitative sensations and linguistic descriptions of quarreling conscious intellects on Earth. Trying desperately to represent with such the lost Eden of a mind-independent or metaphysical existence. Rather hopelessly, though, since a noisy splattering of the former's skull meat -- so as to return to that Eden in the most crude manner, simply reveals the latter to lack any features of experience and reflective thought. Absence, nothingness, oblivion, emptiness, etc, encountered after death. Or at least so one could safely proclaim around the campfires of anti-panpsychism. Despite the occasions of "I don't remember any damn thing!" from some revived dead people, being drowned out by the media-celebrated throng which report tunnels of light and reunions with deceased significant others.